Thickening of deformation-distorted high-angle grain boundaries in nanomaterials

A theoretical model describing deformation-distorted (nonequilibrium) high-angle grain boundaries in nanocrystalline and ultrafine-grained materials has been proposed. Within this model, the dislocation structure of the distorted high-angle grain boundaries has been considered as a combination of the standard wall of grain-boundary dislocations and lattice dislocations (nonequilibrium dislocations) trapped from the adjacent grains. The energy characteristics of a system of grain-boundary defects have been calculated. It has been shown that the thickening of a grain boundary due to the coordinated motion of nonequilibrium dislocations is an energetically favorable and barrierless process. The dependences of the thickening on different parameters of the problem have been investigated. Typical values of the thickening are equal to 1.5–2.5 nm, which agrees with the available experimental data.